Ni-rich cathode materials have attracted wide attention on account of their high specific capacity. However, the poor cycle retention of Ni-rich cathode materials, especially at high voltage or high temperature, is recognized as the main obstacle for extensive commercialization. In this research, we propose a new strategy of doping NCM622 (LiNi 0.6 Co 0.2 Mn 0.2 O 2 ) with Ta 5+ to improve the structural stability due to the high Ta−O dissociation bond energy. XRD refinement results indicate that almost all Ta 5+ are located in Li sites to play a pillar role and cation mixing is inhibited. Electrochemical impedance spectroscopy results show that the increase of charge transfer impedance during the cycling process is controlled. Owing to the stable structure, NCM622 with 0.25% Ta doping exhibits a capacity of 148.1 mAh g −1 with retention reaching 83.6% at 1 C over 3.0−4.5 V after 100 cycles, whereas the bare NCM622 only delivers 143.4 mAh g −1 with a retention of 80.1%. The above results signify that moderate Ta doping is a facile yet effective strategy to develop high-performance Ni-rich cathode materials.

Tungsten oxide as an alternative to conventional acidic PEDOT:PSS has attracted much attention in organic solar cells (OSCs). However, the vacuum-processed WO layer and high-temperature sol-gel hydrolyzed WO are incompatible with large-scale manufacturing of OSCs. Here, we report for the first time that a specific tungsten oxide WO (WO) nanowire can function well as the anode buffer layer. The nw-WO film exhibits a high optical transparency. The power conversion efficiency (PCE) of OSCs based on three typical polymer active layers PTB7:PCBM, PTB7-Th:PCBM, and PDBT-T1:PCBM with nw-WO layer were improved significantly from 7.27 to 8.23%, from 8.44 to 9.30%, and from 8.45 to 9.09%, respectively compared to devices with PEDOT:PSS. Moreover, the photovoltaic performance of OSCs based on small molecule p-DTS(FBTTh):PCBM active layer was also enhanced with the incorporation of nw-WO. The enhanced performance is mainly attributed to the improved short-circuit current density (J), which benefits from the oxygen vacancies and the surface apophyses for better charge extraction. Furthermore, OSCs based on nw-WO show obviously improved ambient stability compared to devices with PEDOT:PSS layer. The results suggest that nw-WO is a promising candidate for the anode buffer layer materials in organic solar cells.

As a kind of Ni-rich cathode material, LiNi0.8Co0.15Al0.05O2 undergoes severe phase transition when cycling under a high cutoff voltage, causing a sharp decline in reversible capacity. In this study, we synthesize LiNi0.8Co0.15Al0.05O2 with a range of Ti doping contents through a facile solid state approach. When the doping content is 1 mol %, it can still deliver a discharge capacity of 179.6 mAh g–1 after 200 cycles at 3.0–4.5 V, with a capacity retention of 97.4%, in comparison with 167.3 mAh g–1 and 89.2%, respectively, for pristine LiNi0.8Co0.15Al0.05O2. Various morphological and structural characterizations are performed to thoroughly comprehend the excellent cyclic performance of Ti-doped LiNi0.8Co0.15Al0.05O2. High resolution transmission electron microscopy images in combination with powder X-ray diffraction patterns illustrate that Ti dopant effectively suppresses the undesirable phase transition. Electrochemical impedance spectroscopy results confirm a relatively low increase of charge transfer impedance, and differential capacity versus voltage curves show a more moderate polarization during cycling. When LiNi0.8Co0.15Al0.05O2 cycles under a high cutoff voltage, the appropriate amount of Ti doping plays a role in stabilizing the structure and relieving the surface deterioration, which proves to be the key to the extremely superior cyclic performance even at 4.5 V.

Single-crystal LiNi1–x–y Co x Mn y O2 cathode materials can effectively suppress intergranular cracks that usually is seen in commercial polycrystal LiNi1–x–y Co x Mn y O2 cathode materials. However, the surface structure degradation for single-crystal LiNi1–x–y Co x Mn y O2 cathode materials is still aggravated at a higher cutoff voltage (over 4.5 V). In this work, we prepare single-crystal LiNi0.6Co0.2Mn0.2O2 cathode materials via a solid-state method and then coat an ultrathin Li–Si–O layer on their surface by a wet coating method. The results show that the single-crystal LiNi0.6Co0.2Mn0.2O2 cathode materials with a Li–Si–O coating layer deliver excellent cycling performance even at a higher cutoff voltage of 4.5 V. The optimized Li–Si–O-modified sample displays a capacity retention of 90.6% after 100 cycles, whereas only 68.0% for unmodified single-crystal LiNi0.6Co0.2Mn0.2O2. Further analysis of the cycled electrodes reveals that the surface structure degradation is the main reason for the decrease of electrochemical performance of single-crystal LiNi0.6Co0.2Mn0.2O2 at a high voltage (4.5 V). In contrast, with Li–Si–O coating, this phenomenon can be suppressed effectively to maintain interfacial stability and prolong the cycling life.

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The interface problem caused by the contact between the electrodes and the solid electrolyte was the main factor hindering the development of solid-state batteries. To enhance the electrode|solid electrolyte interface property, we designed a hybrid electrolyte, the combination of x vol % Li 1.3 Al 0.3 Ti 1.7 (PO 4 ) 3 (LATP) inorganic solid electrolyte and 1 − x vol % liquid organic electrolyte (LE). In this work, the 1 − x vol % LE was dropped between the electrode and the solid electrolyte, and it is found that the electrochemical performance of the LiFePO 4 |Li solid−liquid hybrid battery is significantly improved. At the current density of 0.1 and 0.5 C, the LATP with 15% liquid organic electrolyte could deliver a specific capacity of 160.5 and 124.3 mAh g −1 , respectively; moreover, the specific discharge capacity remained as high as 111 mAh g −1 at 0.5 C after 100 cycles, indicating that the larger interface impedance was eliminated. The LE may have three functions: (1) forming a solid−liquid electrolyte interphase on the surface of the LATP particles to prevent further reduction of LATP, (2) wetting the electrode and solid electrolyte to reduce the interface resistance, and (3) improving interfacial Li-ion transport.

A novel nonconjugated polymer named poly(2-acrylamido-2-methyl-1-propanesulfonic acid sodium salt) (PAMPS-Na) was designed and synthesized. The PAMPS-Na has good solubility in polar solvents, such as water, methanol, and ethanol, which can be used as the cathode buffer layer in organic solar cells (OSCs) through solution processing without damaging the underlying active layer. Moreover, it was found that PAMPS-Na can significantly decrease the Al work function when it was modified with Al. To reveal its universal application in organic photovoltaic devices, a variety of photovoltaic donor materials, including two medium-band gap polymers, a wide-band gap polymer, and a small molecule donor were employed to fabricate OSCs. Compared with OSCs with Ca/Al electrode, the devices based on PAMPS-Na/Al exhibited higher photovoltaic performance, mainly because of the increased short-circuit current. Additionally, OSCs with PAMPS-Na/Al displayed better ambient stability than devices with Ca/Al. It is also interesting to find that the performance of the devices can tolerate a wide change of PAMPS-Na's thickness, enabling the potential for large-scale fabrication of OSCs. The results suggest that PAMPS-Na is a promising candidate as the cathode buffer layer to improve the efficiency and stability of OSCs.

More and more attention has been focused on Ni-rich ternary materials due to their superior specific capacity, but they still suffer inherent structural irreversibility and rapid capacity degradation under a high voltage. Oxidation of unstable oxygen will lead to the irreversible transformation of the structure. Taking into account the strong W–O bond, an appropriate amount of W-doping is studied to reinforce the thermal stability and electrochemical performance of LiNi0.6Co0.2Mn0.2O2 (NCM622) at 4.5 V. Combining experiments and theoretical calculations, it can be found that W-doping is most preferred at Co sites, and the average charge around O in the NiO6 octahedron becomes more negative after W-doping, which can successfully restrain the release of oxygen, thereby improving the stability of the crystal structure during deep delithiation. In addition, W-doping decreases the energy barrier of the Li+ migration slightly and boosts the kinetic diffusion of lithium ions. As a result, NCM622 doped with 0.5% W boasts an outstanding capacity retention of 96.7% at 1 C after 100 cycles and a discharge specific capacity of up to 152.8 mA h g–1 at 5 C between 3.0 and 4.5 V. Furthermore, analysis of the cycled electrodes indicates that the lattice expansion and the formation of microcracks during long cycling are suppressed after W-doping, thereby elevating the structure and interface stability. Therefore, doping an appropriate amount of W via simple methods is helpful to obtain Ni-rich cathode materials with admirable performance.